The overall objective of this proposal is to establish a network site at the National Jewish Medical and Research Center for participation in the Pediatric Asthma Clinical Research Network (PedACRN). National Jewish is an established childhood asthma research center with a strong local, regional and national referral base. The National Jewish site has over 5,000 outpatient clinic visits per year and over 750 subjects have enrolled in clinical studies. Investigators also have ready access to patients in network outpatient clinics and pediatric practices in the community. The Principal Investigators for this program will be Stanley J. Szefler, M.D. and Gary Larsen, M.D, who are nationally recognized leaders in clinical investigations in childhood asthma related to understanding the pathogenesis of asthma and the effect of various therapeutic interventions. Increasing prevalence and morbidity of childhood asthma has been recognized throughout the world. New developments point to the benefits of early intervention with long-term controllers, such as inhaled glucocorticoids, and their potential effect on altering disease progression. There is a critical need to understand the nature of the long-term effects of chronic airway inflammation along with the benefits and risks of available and promising new therapeutic interventions. The National Jewish site will introduce two protocols to the PedACRN. The first is a short-term cross-over study to evaluate the comparative effects of a selected inhaled glucocorticoid and a leukotriene modifier in asthmatic children, ages 3 to 12 years. The differences between responders and non-responders to each medication will be examined incorporating new techniques for measuring pulmonary function in young children, pharmacogenetics, and markers of inflammation. The second is a long term trial to carefully examine the effect of a selected inhaled glucocorticoid and a leukotriene modifier on altering the progression of asthma. Asthmatic children, ages 3 to 6 years, will be enrolled and followed for three years along with a four-month wash-out phase. The National Jewish site will add strength to the PedACRN Network with experience in research network organization, study design, pharmacology, pulmonary medicine, and patient recruitment and orientation to study participation. The PedACRN, in turn, will provide a unique opportunity to design and conduct multicenter clinical trials to address critical issues in the management of childhood asthma.